* Module coding style consistency.
* handle_SubscriptionEvent(): We're always guaranteed to get a language from a
member, since lookup falls back ultimately to the system preferences. So
this method can be simplified.
* Bump up code coverage for several modules.

* New events:
- ConfirmationNeededEvent is triggered when a pendable requiring
confirmation is created. This allows us to define an event handler for
this event which sends the user notification.
- SubscriptionEvent is triggered when a member is added to a mailing list.
This lets us define an event handler which sends the welcome message.
* send_welcome_message() now takes a member parameter instead of an address,
which lets us directly access the member's delivery mode and user display
name (if the member has a user, which it might not in some cases).
* Use the list id in the pendable record instead of the list name for
robustness (the latter can change but the former is permanent).
* Test more registration conditions.
* In the bin/runner command line switch handling, default `verbose` to None
instead of False. This makes it work better with nose's -E switch (log to
stderr).
* In call_api(), if a POST, PUT, or PATCH method is used and data is None,
encode the empty dictionary; seems like the behavior of urlencode() has
changed, so this is safer.
* Fix style and pyflakes warnings.